UNDERSTANDING GENOTYPE AND PHENOTYPE

 

Name:    UNDERSTANDING GENOTYPE AND PHENOTYPE

Activity:                Students will get a bag of shells from two beaches, sort them, identify them and look at variations.

Level:                    3

Developer:         Alberto Mimo                                                                                                   

Site:                       Classroom or Laboratory with access to a computer and excel.

Subjects:             Genetics, statistical analyses.

 

Introduction

Darwin and Russell in the 1800’s were interested in understanding how new species came about. They concluded that somehow random changes in their phenotype were best adapted to an environment or situation and those organisms that did not fit would die out, or lived at a disadvantage because they were not well fitted to the new condition. This is in essence the idea of evolution based on natural selection due to the survival of the best-fitted animal or plant. At the same time, a man named Jean-Baptiste Lamarck theorized that animals evolved by the force of adapting themselves to a new environment and changing their phenotype. Long-neck giraffes get longer necks by trying to reach the leaves on the taller trees. In this lesson, we explore the idea of phenotypic plasticity based on environmental conditions or contact with other species

A living organism’s DNA contains the information that will be transferred to its progeny. Some information is not shown physically or physiologically, but it is all there in their genome. Some of the information is displayed in every organism either in its shape or form or in its physiology. (Read about Gregor Mender,  1822-1884) One is called the organism’s genotype and the other is the organism's phenotype.

Organisms within a species are not always exactly alike, there is a variation within each species that refers back to the exact genome they have. In people, some kids have blue eyes and some dark brown, but this variability has to be all accounted for unless there has been a mutation. Mutation could lead to new species, but that is only when that mutation shows to provide that organism with an advantage. See Darwin and Russel's theory of Evolution.

Variability within one species could have been led by small changes in the habitat, other species' competition, or a predator/ prey relationship. (Anurag A. Agrawal in his paper “Phenotypic Plasticity in the Interactions and Evolution of Species”) Published by the Journal of Ecology in 2001 shows how these changes can be derived from competition, mutualism, predation risk, and parasitism/herbivore or food quality.

Thomas J. DeWitt, Andrew Sih, and David Sloan Wilson in their paper “Cost and limits of phenotypic plasticity” Trends in Ecology & Evolution, 1998, discuss the idea that variations on an organism's phenotype have limits and cost. Some of this cost includes Maintenance and Production of the Phenotypic Change, Information Acquisition Cost, Development Instability, and Genetic Cost, but at the same time, there is a benefit of survival.

Some of the terminologies associated with phenotypic plasticity are: (Phenotypic Plasticity and the origin of diversity. Mary Jane West-Eberhand, Annu. Rev. Ecol. Sust. 1989 20:249-78).

• Alternative phenotypes: Two or more forms of behavior, physiological response, or structure maintained in the same life stage in a single population and not simultaneously expressed in the individual.
• Conditional (or condition – sensitivity): The alternative adopted by a particular individual or at a particular time depends on environmental conditions.
• Allelic-Switch: The alternative adopted by a particular individual depends on the allele(s) present at one or more genetic switch loci.
• Combine switch: The alternative adopted depends on a combination of allelic and environmental factors.
• Polyphenism: The existence of environmental-cued alternative phenotypes in a population.
• Polymorphism: The existence of morphological district alternatives in a population (usually: “allelic-switch alternatives”.

 

Hypothesis

Slipper Shells live at the bottom of the Long Island Sound.  They form a tight community of shells at the bottom of the seawater and are constantly subject to being swept away by the current caused by the incoming and outgoing tides. In areas with narrow channels the effort by the shells to stay in place is greater and in more level areas where the current is less strong the effort of the shells is also less.  The speed of the water at different locations within the Sound changes depending on the site, for example, areas located at the entrance of the sound called the race have stronger currents.

The hypothesis here is that at locations where the speed of the water current is high; shells will transform their shape to be more flat reducing the friction with the water. Shells that live in more tranquil areas will be shaped more bumped or higher in the top. So we have two possible different phenotype shapes on these shells. The idea here is to take measurements and see if we can find differences within collection sites. Have C. fornicata shells a phenotypic plasticity?

Read Phenotypic Plasticity and the Origen Of Diversity. Mary Jane West-Eberhard. Annu. Rev. Ecol . Syst. 1989. 20:249-78

Natural History and Anatomy of the Slipper Shell (Crepidula fornicata L.)

Slipper Shells live out in the bottom of the Long Island Sound. They are found in amazing quantities and compete for habitat with oysters and other organisms. These mollusks stack one on top of the other forming a thick layer. During reproduction, they form clusters where the ones at the bottom are females and the ones on top are males. The eggs are found in sacks that are fertilized in the water and released. These organisms are hermaphroditic, so they change sex as they grow. Starting as males and growing into a female, they live for about 7 to 10 years. You can count the number of growth rings. When they die they are carried away by the tide and the water current. They have very few predators so they are a nightmare to the oyster industry.

A cluster of Slipper Shells from the bottom of the LIS (Long Island Sound) mixed with mud from the site. These shells were collected using a drudge from a science vessel. (Next 3 pictures)

                  

 

Mud and shells covers the see floor

 

Some are on top of other; the lower one is a female

See diagram for their anatomy.

 

Anatomy of the slipper shell

Slipper shells do not move much, they crawl at the beginning but once they find the perfect spot they attach permanently. Their typical food is plankton and other particulate organic matter. Their growth rate is between 0.04 to 1.11 mm/day.

Their abundance can be up to 4,770 individuals per m2. They prefer a substrate made up of small boulders, and muddy gravel and they live at the sublittoral fringe where they are sheltered. Their preference is a salinity of 18 to 40 milligrams per centiliter and a water flow of 1 to 3 knots.

Sites for your Collection

You can collect anywhere there are slipper shells but I have included three sites that are located somewhere south of the state, Coastal Center at Milford Pont, a north site at Hammonassett Beach State Park in Madison, and one additional site at the Race of the Long Island Sound at Watch Hill Cove in Rhode Island. It would be best to do this research on-site without taking the shells to school. These slipper shells form the natural habitat of the area.

 

Sites for your Collection

You can collect anywhere there are slipper shells but I have included three sites that are located somewhere south of the state, Coastal Center at Milford Pont, a north site at Hammonassett Beach State Park in Madison and one additional site at the race of the Long Island Sound at Watch Hill Cove in Rhode Island. It would be best to do this research on site without taking the shells to school. These slipper shells form the natural habitat of the area.

Site One

Costal Center at Milford Point

 

Site two

Hammonasset Beach State Park Meigs point

 

 

Site three

Watch Hill Cove, in Rhode Island

Where do the dead shells come from in your collection?

Where do the dead shells come from in your collection?

Before you start your collection you will need to acquire a Scientific Collecting Permit for marine organisms from the CT Department of Energy and Environmental Protection. You can get the forms at their website (https://portal.ct.gov/DEEP). If you intend to take all the measurements at the beach you do not need to get a permit. The scientific collecting permit will cost you $25 and you have to fill out the correct forms.

The shells that you will collect are found on the beach. These are dead shells that were living in the water near your location that for some reason died and washed into the beach by the tides or storms. They are the perfect habitat for Piping Plovers

You need to collect the shells when it is low tide because we also want you to collect a cluster of live shells deposited in the intertidal area by the tide. There should be between 3 and 7 shells that you will use to learn more about the anatomy of the slipper shells. The other slipper shells you are collecting are just shells without the actual animal on them. Just walk close to the water's edge and look for a cluster. There will be several, take only one and throw the others into the water.

Place the cluster into a jar with 70 % alcohol and label it.

 

 

Place the cluster into a jar with 70 % alcohol and label it.

Species: Crepidula fornicata L.

Date:

Location:

Your school name:

Inventorying the beach

Based on the current literature, there are 3 different slipper shells in the Northeast; Crepidula convexa, convexa which is brown with striped or dots of reddish brown, up to 1.3 cm. long, and is less common than other slipper shells; attaches to shells and rock and other hard objects.  There is the Crepidula plana, also known as eastern white slipper shell, pearly white up to 3.3 cm. long often found attached to the underside of horseshoe crab shells and inside large snail shells occupied by hermit crabs. And finally, there is Crepidula fornicata.

Shells accumulated on the beach

Shells accumulated on the beach

Close up of shells

 

Shells clearly left by the tide

Variety of shells on the beach

 

In addition to collecting the slipper shells, we also need to complete an inventory of other organisms found in the same area. A sandy beach about 15 ft. from the high tide line and about 75 feet in linear length parallel to the beach. Remember that many small invertebrates live buried in the sand. Bring a small shovel.

To do this just get several small buckets or plastic bags, one per every two students, and collect just one good specimen, in good shape of every species you see. Sit by the side of the beach and identify the organisms. Make a list. Then take a picture and let them go.

Use the following list to write the length and height of two sets of shells of 45 individuals. Count the rings of 10 shells and each ring is one year. Write the information on the size of this list.

 

To do this just get a number of small buckets or plastic bags, one per every two students and collect just one good specimen, in good shape of every species you see. Sit by the side of the beach and identify the organisms. Make a list. Then take a picture and let them go.

 

Shell number	Age

 

Length and Height measured in mm.

 

Length	Height

 

Measuring each shell

Measure each shell in millimeters using calipers.

 

Length: Largest length of the shell.